Can you add documentation to our readme and integration site to inform developers that the default keychain must be app scoped/that shared access groups are not supported.

[santiagososaroman-dotcom]

Can you add documentation to our readme and integration site to inform developers that the default keychain must be app scoped/that shared access groups are not supported.

Originally posted by @camden-king in google/GoogleSignIn-iOS#567 (comment)